THE FIRST FLUSH IN SEWER SYSTEMS

The first flush phenomenon of urban wet weather discharges is presentl y a controversial subject. Scientists do not agree with its reality, n or with its influences on the size of treatment works. Those disagreem ents mainly result from the unclear definition of the phenomenon. The objective of this article is first to provide a simple and clear defin ition of the first flush and then to apply it to real data and to obta in results about its appearance frequency. The data originate from the French database based on the quality of urban wet weather discharges. We use 80 events from 7 separately sewered basins, and 117 events fro m 7 combined sewered basins. The main result is that the first flush p henomenon is very scarce, anyway too scarce to be used to elaborate a treatment strategy against pollution generated by urban wet weather di scharges. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.